In optical discs, wobbling grooves are known to be used as additional information such as address information and recording conditions added to data recording tracks. For example, the pickup is placed at a desired track position using a wobbling groove so as to record data to the track or reproduce data therefrom.
On the other hand, illegal copying of content recorded on optical discs has recently become a problem. A sturdy contents protection system (CPS) designed to protect content is required.
Encryption of content to be stored on a disc is an approach to achieving a contents protection system (CPS). A configuration has been proposed that is designed to record, to the grooves, key information used to decrypt encrypted content and other content utilization control information in such a manner that these pieces of information are superimposed on address information. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2004-213781) discloses a configuration designed to record key information to the grooves for use.
However, key information used to decrypt encrypted content and other content utilization control information is confidential and must be protected from easy reading to prevent leaks. On the other hand, if key data is recorded on a disc, it is necessary for the reproducer of a user having a legal content utilization right to accurately read the bits making up the key. The reason for this is that the decline in the bit reading accuracy makes it impossible to obtain accurate key information, thus making it impossible to decrypt the content.
For example, if key information used to decrypt content is recorded in the groove, it is necessary to meet two mutually contradictory requirements, i.e., avoiding easy reading and achieving accurate reading.
Among the requirements that must be met by a configuration adapted to record CPS data such as key information, i.e., data applied to a contents protection system (CPS), to a disc for use are as follows:    1. Highly reliable reproduced CPS data signal    2. Difficult to copy CPS data to other media    3. Not significantly high manufacturing costs of CPS data storage media and recording/reproduction drive
Patent Document 1 (Japanese Patent Laid-Open No. 2004-213781) described above discloses a configuration adapted to record key information in the grooves for use. This prior art incorporates a novel idea to meet the above requirements. On the other hand, however, confidential information decryption techniques have also advanced. As a result, there are demands for a recording configuration offering an even higher degree of privacy.